The primary afferent terminations of the gustatory nerves are located in the nucleus of the solitary tract (NTS). These terminal fields extend in a rostral to caudal direction and are anatomically arranged in a dorsal to ventral fashion with distinct regions of overlap. Both the chorda tympani and glossopharyngeal fields have been identified as regions undergoing considerable plasticity in response to restriction of dietary sodium during development. Sodium deprivation results in expansion of both fields into the territory of adjacent fields increasing the proportion of overlap occurring among the respective fields. We hypothesize that the changes in terminal field morphology induced by dietary sodium restriction are a reflection of changes to the gustatory circuitry of the NTS. In order to elucidate changes occurring between pre- and post synaptic contacts between afferent terminations and NTS relay neurons, the following has been proposed: First, the circuitry between afferent terminal fields and gustatory relay neurons will be viewed using light microscopy and multiple fluorescent labeling techniques in order to elucidate the arrangement of NTS neurons among the gustatory fields and identify differences in terminal field/relay neuron interaction with respect to changes in dietary sodium content. Then, the synaptic morphology of the area will be characterized via electron microscopy, focusing specifically on differences between adult and sodium restricted animals that may correlate with alterations in terminal field formation. The results of these studies will further illuminate the general circuitry of the three gustatory terminal fields as well as provide insight, to the plasticity induced by a low sodium diet. [unreadable] [unreadable]